1. Field of the Invention
The present invention relates to systems and methods for radio navigation, and in particular to a system and method for radio navigation using a spatially resolved antenna.
2. Description of the Related Art
In recent years, there has been an increasing need for remote and mobile location systems. For example, there is a need for cellular telephone (cellphone) systems that can locate users, particularly when the user has dialed 911 or other emergency number. There is also a need to locate large numbers of military or fire personnel who can be located over large areas. Further, this capability must be provided in places where line of sight between locating elements are obscured or compromised by multipath distortions (e.g. environments such as urban locations and rugged terrain). These factors limit the accuracy and hence, the usefulness of the location system.
There is further a need to provide secure communications between large numbers of widely distributed receiving/transmitting agents. One way to accomplish this feat is through the use of narrow beam communication signals directed at the intended recipient of the message. Unfortunately this requires accurate information regarding the location of the intended recipient relative to the location of the transmitting agent
What is needed is an accurate, but inexpensive location system that provides adequate location accuracy and availability even in environments that are ordinarily not suitable for radio location. The present invention satisfies that need.
To address the requirements described above, the present invention discloses a method, apparatus, article of manufacture, of radio navigation among a plurality of stations S0, S1, . . . , Si. The method comprises the steps of propagating a state "PHgr"0 of a first station S0 according to autonomous, or self-contained, inertial measurements, wherein the state "PHgr"0 includes the position P0[x0,y0] of the first station, wherein x0 is the position of the first station along a first axis, and y0 is the position of the first station along a second axis orthogonal to the first axis, receiving a signal in the first station S0 and resolving the received signal to at least one angular sector xcex8 in a plane formed by the first axis x and the second axis y, the received signal comprising first information describing an estimated state "PHgr"1 of a second station S1, wherein the state "PHgr"1 includes a position P1[x0,y0] of the second station S1, and estimating the state "PHgr"0 of the first station S0 at least in part from the propagated state {dot over ("PHgr")}0, the resolved angular sector and the relative range R10 of the second station S1 and the first information. The apparatus comprises an inertial reference unit for generating inertial measurements of a state of the first station, a navigation module, for propagating the state "PHgr"0 of the first station S0 based upon the inertial measurements wherein the state "PHgr"0 includes the position P0[x0,y0] of the first station, wherein x0 is the position of the first station along a first axis, and y0 is the position of the first station along a second axis orthogonal to the first axis, at least one antenna communicatively coupled to a receiver for receiving a signal comprising first information describing an estimated state "PHgr"1 of a second station S1, wherein the state "PHgr"0 includes a position P1[x0,y0] of the second station S2, a resolver, for resolving the received signal to at least one angular sector xcex8 in a plane formed by the first axis x and the second axis y and radio rangefinder for measuring R10, the relative range of the second station S1 with respect to the first station, S0 The navigation module further estimates the state "PHgr"0 of the first station S0 at least in part from the propagated state {dot over ("PHgr")}0, the resolved angular sector xcex8, relative range R10 and the first information.
The foregoing provides location services in environments without a line of sight between elements, and mitigates multipath and signal attenuation problems from nearby structures and terrain features.